Various prior art shielding materials are presently used for preventing the leakage and infiltration of electromagnetic waves through the gap between an edge, defining an opening in a housing of an electrical apparatus, and a lid for closing the opening or a part for connecting the housing and the lid.
For example, the U.S. Pat. No. 4,857,668 proposes a gasket in the form of an electrically conductive sheath attached around a bar-shaped elastic core. If such a gasket is deformed when attached to a curved or bent part, however, the surface of the gasket becomes creased, thereby producing gaps between the gasket surface and the part to which the gasket is attached. A gap between a housing and a corresponding lid, for example, cannot be securely sealed by such a gasket. Therefore, this type of gasket cannot be effectively used on curved or bent parts.
Another shielding material is described in the Japanese examined and published utility model application No. 2-34880. The disclosed shielding material is formed by sewing electrically conductive threads to an elastomeric sheet consisting of silicone rubber or other elastic material. When this type of shield material is attached to the housing of electronic components, the electrically conductive threads sewn to the elastomeric sheet continuously engaging with both the housing and the lid between which the shielding material is mounted. This ensures a continuous electrical path through the gap between the housing and the lid, thereby protecting the gap against the passage of electromagnetic waves. Moreover, even if the elastomeric sheet is deformed and creased, the electrically conductive threads do not become creased. Therefore, the shielding material deforms, conforming to the configuration of the part to which the material is attached without creasing.
Shield material attached to an edge defining an opening in a housing or other part has to shield against passage of electromagnetic waves through the gap between the housing and the lid or infiltration of electromagnetic waves through the side surface of the elastomeric sheet. In the prior art shielding material, only the electrically conductive threads sewn through the elastomeric sheet form a shielding layer for shielding against electromagnetic waves entering from the side surface of the elastomeric sheet. Moreover, the electrically conductive threads in this layer are only stitched at discrete intervals. Therefore, in order to provide sufficient shielding effectiveness, the electrically conductive threads have to be closely stitched, forming a plurality of closely spaced shielding layers. Such a solution increases the number of stitches in the substrate, thereby deteriorating the strength of the substrate.